Problem: Daniel is 2 years older than Gabriela. Three years ago, Daniel was 3 times as old as Gabriela. How old is Gabriela now?
Solution: We can use the given information to write down two equations that describe the ages of Daniel and Gabriela. Let Daniel's current age be $d$ and Gabriela's current age be $g$ The information in the first sentence can be expressed in the following equation: $d = g + 2$ Three years ago, Daniel was $d - 3$ years old, and Gabriela was $g - 3$ years old. The information in the second sentence can be expressed in the following equation: $d - 3 = 3(g - 3)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $g$ , it might be easiest to use our first equation for $d$ and substitute it into our second equation. Our first equation is: $d = g + 2$ . Substituting this into our second equation, we get the equation: $(g + 2)$ $-$ $3 = 3(g - 3)$ which combines the information about $g$ from both of our original equations. Simplifying both sides of this equation, we get: $g - 1 = 3 g - 9$ Solving for $g$ , we get: $2 g = 8$ $g = 4$.